Improvement in processes of producing photo-relief plates for printing



UNITED STATES PATENT QFFICE.

LOUIS E. LEVY AND DAVID BACHRAGELJR, OF BALTIMORE, MARYLAND.

IMPROVEMENT IN PROCESSES 0F PRODUCING PHOTO-RELIEF PLATES FOR PRINTING, 85c.

Specification forming partof Letters Patent No. 169,104, dated January 26,1875; application filed January 4, 1875. a

To all whom it may concern:

Be it known'that we, LOUIS EDWARD LEVY and DAVID BAGHRACH, J r., both of the city of Baltimore, Maryland, have invented an Improvement in Photo Mechanical Printing, which improvementwe term the Levytype, consisting of a method of preparin g relief-plates, from which copies may be printed in the ordinary typographic press.

The process by which these .plates are prepared has for its basis the fact (which has been well known for some years past) that gelatine, glue, and allied substances, when mixed in solution with an alkaline chromate, such as the bichromate of potassium or ammonium, become sensitive to light. This fact has heretot'ore been largely taken advantage of in" the graphic arts, and has givenrise to numerous processes by which the sensitiveness of the chrome-gelatine film is utilized. Thus, photo-lithography and photo-zincography have come into extensive use, and various modifications of these are well known. These, and such kindred processes as the Albertype, the Woodburytype,andothers,'require verycareful manipulation, skill,and experience to obtain results after the photographic and purely chemical work is finished,and are, moreover, almost as slow, and often as expensive, as ordinary silver prints. Their great advantage lies in the fact that the printing may proceed independent of solar light, and that the results are more permanent.

Many attempts have been made, of which som e have succeeded-only, however, in skilled hands-to utilize the sensitiveness of the chrome-gelatine film for the attainment of the photographic image in relief. Various methods are known and in use. One is by the transfer of the inked image to zinc, and the etching of the latter in the uncovered portions. Another proceeds upon the basis of getting a cast from the smaller image, and a stereotype from the cast. And still another is based upon the washing out of the unaffected portions of the film, and either pressing the dried film into soft metal, or taking caoutchouc or plaster casts from the film while still wet. Washing out the film, and then etching, has also been tried 5 and, lastly, etchingdirectlythrough the unaffected portions of the film without washing them away has been attempted with more 'or less success. All these processes entail the necessity of surmounting many 'difliculties which bar the way to complete success. This is to be attained only by dint of expert enced manipulation and favorable circumstances; and, in conse uence, these processes have none of them co e into very general use. They are being made ommerciall y available, but only in the hands f a very few individuals and corporations, ho are able to control the necessary skill an capital.

Very long ago, by Paul Pretsch, in Vienna,

- and by others since and elsewhere, eiforts have been made to obtain an electrotype copy-of the swollen image. This process aflords the most direct and simple means for the attainment of the fixed relief image, insomuch as only two distinct operations are requisite, both of which are purely chemical, and therefore require no long-acquired manual dexterity. These two operations are, the obtaining the relief image on the gelatine plate in proper shape and condition, and, second, the getting ot'nn electrotype upon this relief. Simple and few, however, as are the conditions requisite to success, this desideratum has hitherto not been attained.- In the preparation of the film three great obstacles had to be overcome primarily, and another one secondarily. Primarily- First. The portion intended to receive the ink required to be on a plane. Instead ofbeing thus obtained, they were invariably on different planes, some portions being in high, and other portions in low, relief.

Second. The relief required to be of sufficient altitude to preclude the possibility of other parts than those intended to print from receiving the ink, and thus blotching the paper; and, I

Third. The film required to he electrolytic,

so as to receive the copper deposit in the elecfro-chemical bath. This was attained by the deposition of gold or silver by various methods, but with only partial success. Plumbago, also, has been tried, but with similar results. The consequence was, that when a deposit was obtained it was generally spongy and full of holes. These, among others, have been dilficulties to be surmounted in the preparation of the film itself, without reference to one great difficulty which manifested itself when the film was suspended in the electrotype-bath. Here the various operations which the film had undergone had brought it into a condition to be affected by the copper solution, which either separated the film entirely from its support, or tended more or less to liquefy it, sometimes quite distorting the film out of all shape, and, under some conditions,

' more or less completely dissolving it. In consequence of all these serious .obstacles, this, the simplest of all photo-mechanical processes, has never heretofore been practically available.

In the process hereinafter described, and for which we desire to obtain Letters Patent, all of these difficulties have severally been overcome.

We now specify the various stepsof our process, as follows:

First. Gelatine is dissolved in water to the consistence of a thick jelly, solid at ordinary temperatures. When required for use, the solution is-liquefied by heat. .To this solution is added a saturated solution of bichromate of potassium or ammonium, or its equivalent in rendering the organic substance of the film sensitive to light, in quantity varying with the temperature, and with :the class of work required to be produced.

Second. This mixed solution is now spread upon glass plates which have been thoroughly cleaned, and poured on until a thick lay'ercovers the glass evenly over the whole surface. The thickness of the layer depends ,upon the general character of the work for which it is intendedgthe greater the relief required the thicker should be the film. It should. however, even for the most uniform work, be of considerable thickness. .This is allowed to dry, either spontaneously, by ordinary evaporation, or by being placed in an oven and heated moderately until hard.

Third. This film is now exposed, under a negative of adequate density, such as are generally. used in printing copies of line engravings, to solar light. Care must be taken to have the rays of light reach the negative directly from the perpendicular. To this end side light must be excluded, so as to prevent the film from being affected by diagonal rays. The amount of exposure'to light is an important element in this process. This exposure can scarcely be too prolonged; it should be at least half an hour to direct sunlight. Portions intended to remain white may be protected byan opaque covering or coating on the negative. Two, three, and even five hours exposure to diffused-light (reaching the negative through a long box) is needed to complete the requisite action. Thisis to insure the complete reduction of the bichromateto chromic acid, thus securing the most perfect insolubility of the exposed portions of the sensitive film, even in the finer details of the picture, and thus to keep all the lines on one plane.

Fourth. After exposure of the film the edges of the plate are provided with a-rim of melted wax, which is to prevent the film from peeling from the glass by the continuance of any accidental peeling at the edges.

Fifth. To partially swell the film'it is now soaked in cold water, but only during a limited space of time, dependent upon the thickness of the film and the quantity of bichromate 'used in sensitizing it, with the view of retainin g a quantity of the bichromate as a base for the next subsequent operation.

Sixth. The film, still retaining a quantity of the bichromate, is then taken out and plunged into a solution of nitrate of silver. Here the swelling is completed, which condition is indicated by the chromic acid in the affected portions showing marked signs of reddening. The silver solution, while increasing the relief, adds greatly to the sharpness of the same, and the resulting bichromate of silver affords the requisite basis for the subsequent operations.

Seventh. It is now washed under a tap, and immediately plunged into a solution of the sulphate of iron in water. This solution is acidulated, to enable the reduction of the metallic deposit to proceed more freely. The action of the iron solution is allowed to continue until the picture is plainly visible from the back of the glass in red lines upon a gray or' dark ground. A metallic substratum is thusobtained, which is homogeneous throughout the entire thickness of the film, instead of being a mere surface-deposit. This is an essential element to'the success of the work, and must be fully carried out. It has another important efi'ect upon the film, insomuch as'it coagulates or tans it, rendering it capableof enduring unaltered through the subsequent operations.

Eighth. When taken from the iron solution the plate is copiously washed under a tap, and immediately flowed with a dilute solution of the sulphuret of potassium. This application turns the film to a black color, consequent upon the reduction to the sulphuret of silver, and the action of the solution is continued until the entire deposit of metallic silver is uniformly reduced to a sulphuret.

Ninth. In this condition the film is sufiiciently electrolytic for all practical purposes. It may now be hung in the electrotype-bath, and there receive the metallic deposit of cop per.

Tenth. To insure the easy and more rapid action of the battery we cover the sulphureted film, aft-er drying, with a coating'of plumbago. The dried sulphureted film receives the plumbago with the greatest facility, and it may be brushed on and polished as easily as on wax.

Eleventh. The plate is now attached to a wire or other suitable arrangement by which it may be connected in the precipitating-trough with the positive pole of the battery. Here it receives the deposit, which may be com pleted with more or less rapidity, according to the condition of the bath, battery, &c.

Twelfth. In certain conditions of the copper solution the copper shell does not readily leave the following references to details and modifications:

First. Ordinary glue may be used in place of gelatine, being preferable for some kinds of work.

Second. The swelling may he brought about 'in a solution of alum, in a solution of the .per-

sulphate of iron, in a solution of tannic acid, and in other solutions and liquids, and the silver deposit be afterward precipitated.

Having described our invention, we claim the following: i

1. In the preparation of photo-relief plates for printing, &c., the described process of effecting the complete swelling of the gelatine film as a continuous operation, after being partially swollen in water, by treatment with the nitrate-ofsilver solution, substantially in the manner and for the purpose set forth.

2. The described process of producing the deposit of metallic, silver on the surface and in the body of the gelatine film, in the manner and for the purpose substantially as set'forth.

3. The described method of producing an electrolytic deposit of sulphuret of silver by means of sulphuret of potassium,substantially in the manner and for the purpose set forth.

4. The described process of producing reliefplates for printing and other purposes, consisting essentially of the several steps above described, in the order of their succession, substantially as set forth.

LOUIS E. LEVY. 7 DAVID .BAOHRAOH, JR. Witnesses:

E. J. SWEET, E. H. THOMAS. 

